Nautilus
The nautilus is a marine mollusk belonging to the cephalopod subclass Nautiloidea, which includes the only extant cephalopods with an external shell. Here are some detailed points about nautiluses:
Classification
Physical Characteristics
- Shell: The nautilus shell is coiled, chambered, and can grow up to 25 cm in diameter. It is made of aragonite, a type of calcium carbonate.
- Chambers: The shell has numerous chambers which the nautilus can fill with gas or water to control its buoyancy.
- Eyes: Unlike other cephalopods, nautiluses have pinhole eyes, which lack a lens, leading to poor vision.
Biology and Behavior
- Habitat: Nautiluses are found in the Indo-Pacific region, from shallow reefs to depths of around 500 meters.
- Movement: They move by jet propulsion, expelling water through a siphon.
- Reproduction: Nautiluses reproduce by laying eggs which are attached to the substrate. They are known for having a long lifespan, potentially living for over 20 years.
Historical Context
- Fossil Record: The nautilus has an extensive fossil record going back to the Cambrian period, with their ancestors, the ammonites, being much more diverse and numerous in the past.
- Evolutionary Significance: Nautiluses are considered living fossils, having changed little in form over millions of years, providing insight into the evolution of cephalopods.
Conservation
- Nautiluses face threats from habitat destruction, deep-sea trawling, and the shell trade. They are listed in Appendix II of CITES (Convention on International Trade in Endangered Species).
- Research: There is ongoing research to understand their distribution, behavior, and the impact of human activities on their populations.
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